I agree with your general point. A lot of science was needed to create the transistor. But in this particular case, the design of Newcomen's engine is very simple, needs no science beyond the notion of 'hot water expands', and could certainly be comprehended and built by the ancient Greeks and Romans. Of course, it may be that the ancients didn't use (or use up) enough coal to be in need of a mine water pumping solution, and a steam locomotive is rather more complex.